1. Technical Field
The present disclosure is directed to electrosurgical systems, and, in particular, to an electrosurgical system having a radio frequency (RF) output with a current-source type behavior.
2. Description of the Related Art
An electrosurgical generator is used in surgical procedures to deliver electrical energy to the tissue of a patient. When an electrode is connected to the generator, the electrode can be used for cutting, coagulating or sealing the tissue of a patient with high frequency electrical energy. During normal operation, alternating electrical current from the generator flows between an active electrode and a return electrode by passing through the tissue and bodily fluids of a patient.
The electrical energy usually has a waveform shaped to enhance its ability to cut, coagulate or seal tissue. Different waveforms correspond to different modes of operation of the generator, and each mode gives the surgeon various operating advantages. Modes may include cut, coagulate, a blend thereof, desiccate, or spray. A surgeon can easily select and change the different modes of operation as the surgical procedure progresses.
In each mode of operation, the electrosurgical power delivered to the patient is regulated to achieve the desired surgical effect. Applying more electrosurgical power than necessary results in tissue destruction and prolongs healing. Applying less than the desired amount of electrosurgical power inhibits the surgical procedure. Thus, it is desirable to control the output energy from the electrosurgical generator for the type of tissue being treated.
Different types of tissues will be encountered as the surgical procedure progresses and each unique tissue requires more or less power as a function of frequently changing tissue impedance. As different types of tissue and bodily fluids are encountered, the impedance changes and the response time of the electrosurgical control of output power must be rapid enough to seamlessly permit the surgeon to treat the tissue. Moreover, the same tissue type can be desiccated during electrosurgical treatment and thus the tissue impedance will change dramatically in the space of a very brief time. The electrosurgical output power control needs to respond to a rapid change in impedance to effectively treat tissue.
Electrosurgical generators generally have a voltage-source type output behavior. In the voltage-source type output behavior, the delivered output current is inversely proportional to the load (e.g., tissue) impedance. Electrosurgical generator may also have an RF output with a current-source type behavior where the delivered current is independent of the load impedance. An example of an electrosurgical generator with a current-source type behavior may be a current-fed push-pull converter. A current-source type generator has a disadvantage in that, as the impedance of the tissue increases, the open-circuit voltage may reach unacceptably high levels.